In many industries, it is advantageous to heat objects in a desired manner. Often, a flexible heater such as a heating pad, jacket, or jacket is disposed on or about the surface of the object to be heated so that, when activated, the flexible heater elevates the temperature of the object. For an example of such a flexible heater, see U.S. Pat. No. 5,883,364 the disclosure of which is expressly incorporated herein in its entirety by reference.
One application of such flexible heaters is gas cylinders warmers which are used in industries such as, for example, welding, compressed/specialty gas manufacturers, pharmaceutical manufacturers, and semiconductor manufacturers. Heating a gas cylinder creates convection currents to increase pressure inside the cylinder which improves process control (maintains the gas at a desired temperature and pressure) and condensation control (reduces the amount of gas that is condensed within the cylinder and thus wasted). Condensation control is important because using all of the gas in the cylinder reduces wasted gas and saves money. The most common gas that benefits from gas cylinder warmers is SF6 (Sulfur Hexafluoride). However, there are many other gases which can benefit from the use of gas cylinder warmers such as, for example, propane, nitrogen, oxygen, BCl3, WF6, and HF.
While these prior gas cylinder warmers generally perform their intended purpose, they do not always provide a uniform temperature across the gas cylinders when operated in a wide range of ambient temperatures. The prior gas cylinder warmers typically result in temperature profiles having severe hot spots. Uniform heat is ideal for process temperature maintenance and also for gas bake-out (condensation control). Additionally, these gas cylinder warmers typically require the use of a temperature controller. The use of a temperature controller adds cost and complexity to the system and thus it is desirable to avoid use of a temperature controller if possible. Furthermore, these gas cylinder warmers typically cannot be used for in outdoor and or hazardous locations (Class I, Division I, and Group C &D). Accordingly, there is a need in the art for improved gas cylinder warmers.